1. Field of the Invention
The invention relates generally to factors associated with the Wnt/β-catenin signaling pathway and, more specifically, to interaction between transcription components of the pathway, including the SALL protein family and OCT4, which are involved in the regulation of embryonic and cancer stem cells, including methods for the diagnosis and treatment of proliferative disorders by targeting such interaction.
2. Background Information
ES cells derived from the inner cell mass (ICM) of the blastocyst are able to undergo self-renewing cell division and maintain their pluripotency over an indefinite period of time. ES cells can also differentiate into a variety of different cell types when cultured in vitro. The Wnt/β-catenin signaling pathway has been associated with the self-renewal of normal human stem cells (HSCs) and the granulocyte-macrophage progenitors (GMPs) of chronic myeloid leukemia (CML). Further, the transcriptional factor, OCT4, has been identified as a key regulator for the formation of ICM during preimplantation development. Moreover, OCT4 protein seems to plays a central role in maintaining the pluripotency of embryonic stem (ES) cells by regulating a wide range of genes.
The role of stem cells has been considered in the etiology of cancer. There has been increasing evidence that tumors might contain such cancer stems cells, i.e., rare cells that account for the growth of tumors. These rare cells with indefinite proliferative potential may account for the resistance observed for cancer cells in response to conventional therapeutic modalities. It is known that stem cells can be identified in adult tissues, where such cells arise from a specific tissue; e.g., hematopoietic cells. As the self renewal property of stem cells is tightly controlled in normal organogenesis, the de-regulation of self-renewal might result in carcinogenesis.
Myelodysplastic syndrome (MDS), for example, is a hematological disease marked by the accumulation of genomic abnormalities at the hematopoietic stem cell (HSC) level leading to pancytopenia, multilineage differentiation impairment, and bone marrow apoptosis.
Mortality in this disease results from pancytopenia or transformation to acute myeloid leukemia (AML). AML is a hematological cancer characterized by the accumulation of immature myeloid precursors in the bone marrow and peripheral blood.
From the analysis of genetic translocation in bone marrow samples from AML patients, it is clear that transcription factors critical for hematopoiesis play an important role in leukemogenesis. The pathogenesis of AML is considered to involve multistep genetic alternations. Because only HSCs are considered to have the ability to self-renew, they are the best candidates for the accumulation of multistep, preleukemic genetic changes and transforming them into so-called “leukemia stem cells” (LSCs).
Alternatively, downstream progenitors can acquire self-renewal capacity and give rise to leukemia. LSCs are not targeted specifically under current chemotherapy regimens yet such cells have been found to account for drug resistance and leukemia relapse.
The SALL gene family, SALL1, SALL2, SALL3, and SALL4, were originally cloned on the basis of their DNA sequence homology to Drosophila spalt (sal). In Drosophila, spalt is a homeotic gene essential for development of posterior head and anterior tail segments. It plays an important role in tracheal development, terminal differentiation of photoreceptors, and wing vein placement. In humans, the SALL gene family is associated with normal development, as well as tumorigenesis. SALL proteins belong to a group of C2H2 zinc finger transcription factors characterized by multiple finger domains distributed over the entire protein. During the tracheal development of Drosophila, spalt is an activated downstream target of Wingless, a Wnt ortholog. It has been demonstrated that SALL1 interacts with β-catenin by functioning as a coactivator, suggesting that the interaction between SALL and the Wnt/β-catenin pathway is bidirectional.